SimplePetscNonlinearSolver.cpp

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*/

#include <sstream>
#include "petscsnes.h"
#include "SimplePetscNonlinearSolver.hpp"
#include "Exception.hpp"
#include "PetscTools.hpp"

Vec SimplePetscNonlinearSolver::Solve(PetscErrorCode (*pComputeResidual)(SNES,Vec,Vec,void*),
                                      PetscErrorCode (*pComputeJacobian)(SNES,Vec,Mat*,Mat*,MatStructure*,void*),
                                      Vec initialGuess,
                                      unsigned fill,
                                      void* pContext)
{
    SNES snes;

    // Create the residual vector by copying the structure of the initial guess
    Vec residual;
    VecDuplicate(initialGuess, &residual);

    Mat jacobian; // Jacobian Matrix

    PetscInt N; // number of elements

    // Get the size of the Jacobian from the residual
    VecGetSize(initialGuess,&N);

    // Note that the Jacobian matrix might involve new non-zero elements in the course of a SNES solve
    PetscTools::SetupMat(jacobian, N, N, fill, PETSC_DECIDE, PETSC_DECIDE, true, false /*malloc flag*/);

    SNESCreate(PETSC_COMM_WORLD, &snes);
    SNESSetFunction(snes, residual, pComputeResidual, pContext);
    SNESSetJacobian(snes, jacobian, jacobian, pComputeJacobian, pContext);
#if (PETSC_VERSION_MAJOR == 3 && PETSC_VERSION_MINOR >= 4) //PETSc 3.4 or later
    SNESSetType(snes, SNESNEWTONLS);
#else
    SNESSetType(snes, SNESLS);
#endif
    SNESSetTolerances(snes,1.0e-5,1.0e-5,1.0e-5,PETSC_DEFAULT,PETSC_DEFAULT);
#if (PETSC_VERSION_MAJOR == 3 && PETSC_VERSION_MINOR == 3) //PETSc 3.3
    SNESLineSearch linesearch;
    SNESGetSNESLineSearch(snes, &linesearch);
    SNESLineSearchSetType(linesearch, "bt"); //Use backtracking search as default
#endif
#if (PETSC_VERSION_MAJOR == 3 && PETSC_VERSION_MINOR >= 4) //PETSc 3.4 or later
    SNESLineSearch linesearch;
    SNESGetLineSearch(snes, &linesearch);
    SNESLineSearchSetType(linesearch, "bt"); //Use backtracking search as default
#endif

    // x is the iteration vector SNES uses when solving, set equal to initialGuess to start with
    Vec x;
    VecDuplicate(initialGuess, &x);
    VecCopy(initialGuess, x);

#if (PETSC_VERSION_MAJOR == 2 && PETSC_VERSION_MINOR == 2) //PETSc 2.2
    SNESSolve(snes, x);
#else
    SNESSolve(snes, PETSC_NULL, x);
#endif

    PetscTools::Destroy(residual);
    PetscTools::Destroy(jacobian); // Free Jacobian

    SNESConvergedReason reason;
    SNESGetConvergedReason(snes,&reason);
#define COVERAGE_IGNORE
    if (reason < 0)
    {
        std::stringstream reason_stream;
        reason_stream << reason;
        PetscTools::Destroy(x); // Since caller can't free the memory in this case
        SNESDestroy(PETSC_DESTROY_PARAM(snes));
        EXCEPTION("Nonlinear Solver did not converge. PETSc reason code:"
                  +reason_stream.str()+" .");
    }
#undef COVERAGE_IGNORE
    SNESDestroy(PETSC_DESTROY_PARAM(snes));

    return x;
}